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This Wednesday, June 7, 2017 photo shows discarded used hypodermic needles without protective sheaths at an encampment where opioid addicts shoot up along the Merrimack River in Lowell, Mass.

Deaths from heroin and opioid overdoses may have been underreported by more than 20 percent, according to a new study from the University of Virginia.

Researchers looking into the nation's deadly drug overdose epidemic revisited thousands of death certificates between 2008 and 2014 and found that mortality rates for opioids were 24 percent higher than previously reported, while the mortality rate for heroin was 22 percent higher than previously reported, according to NBC News.

"Opioid mortality rate changes were considerably understated in Pennsylvania, Indiana, New Jersey and Arizona," according to the study, published this week in the American Journal of Preventative Medicine. "Increases in heroin death rates were understated in most states, and by large amounts in Pennsylvania, Indiana, New Jersey, Louisiana and Alabama."

The presidential opioid commission, chaired by New Jersey Gov. Chris Christie, has urged President Donald Trump to "declare a national emergency" to deal with the crisis that, according to the National Institute on Drug Abuse, killed nearly 35,000 across the United States since 2015.

New Research Shows Opioid Use On The Rise

A new survey from the National Institute on Drug Abuse reveals in 2015 more than a third of American adults took a prescription painkiller.